Radio and like instruments for use in high-frequency testing research and development



July 31, 1951 W. o. AGAR 2,562,759

RADIO AND LIKE INSTRUMENT FOR usE IN HIGH FREQUENCY TESTING RESEARCH AND DEVELOPMENT Filed Feb. 28, 1947 firmen/5X Patented July 31, 1 951 c RADIO AND LIKE INSTRUMENTS FOR USE IN YHIGH-FREQUENCY TESTING RESEARCH AND DEYELOPMENT William liver Agar, Danbury, England, assignor,

byI mesne assignments, to Radio Corporation I of America, New York, N. Y., a corporation of Y v v Delaware Application February 28,1947, serial No. 731,652 t InGreat Britain February 13, 1946 Section 1, Public Law 690, August 8, 1946 `Patent expires February 13, 1966 i 8-Claims. (Cl. 1754-183) This invention relates to radio and like instrucase the voltage takenjoif from the discriminator ments for use in high frequency testing research circuit (or other means for producing the freand development `and has for its object to provide quency dependent voltage)Y is Vapplied to one and improved instruments capable of providing for thevother voltage takenjoif from the rectifier is oscillographic examination of the behaviour of applied tothe other,of the normally provided muaerials; feeders, television apparatus, radio'comtually perpendicular `deflection systems of the ponents, iilt ers and impedance members generaltube;` i 1y over awide range of frequencies. Preferably also a; portion ofthe output from Considerable diiculty is experienced and much the filter is employed: for automatic volume contime s pent Yin the design and development-testing 10 trol of one or bothV oscillators-the most conof Vapparatus required to operate uniformly or in venientarrangement is-AVC of the xed oscillator accordance with a Vpredetermined characteristic only-to maintain substantially constant ampliover a wide frequency band. For example it may tude at the output'terminals vof the filter. easily take monthsof intensive work to develop, The invention is illustrated in the accompanywith the aidjof the ordinaryhigh frequency bridge ing diagrammatic drawing which shows a premeasu'ring apparatusfa'satisfactory transmitting ferred embodiment of the invention as applied to aerial to cover an abnormally wide band such, an instrument operatingin a continuous manner for example, -as the band 1 to 20 mc./s. with subover a frequency range of 1 to 21 mc./s. It is to stantially at impedance curve, it being necesbe understood, however, that the values of freu sary, withsuch apparatus, to plot the impedance quencies and other quantitative data given are s tep by step' over the frequency range, made purely by way of example and that the invention Whatever design changes may beindicated by is inno Sense limited tilereioy.,V these tests, repeat the tests-and so on until a Referring to the drawiner vthe Output from a satisfactory result is achieved. The present iniixed frequency discharge tube oscillator l opervention seeks to provide animproved test or deating at 39 inc/s. is fed as one input to av disvelopment instrument which is much quicker to charge tube mixer stage'2 of any convenient deusejin a case such asV that just envisaged' than sign well known per se. The Second input t0 the the normal high frequency ,test gear of bridge mixer stage is provided by a variable frequency type.A discharge tube oscillator 3 capable of producing Accordingvto this invention a radio or like test any frequency between 40 and 60 mc;/s. in depend- I or development instrument comprises in combience upon the setting of its tuning condenser.

nation a fixed frequency oscillator, a variable fre- This condenser is preferably of the so-called quency oscillator, means for continuously and "butterf1y rotary/vane type and is continuously cyclically varying thegfre'quency of the variable rotated by an-electricinotor'ilV at',1say90 R. P. M. oscillator over a predetermined range, a mixer Since, with this typeo f; condenser, the frequency stage fed from the two oscillators, a filter fed of oscillationwill varyffrom maximum to minifron'fthe mixer stage and adapted to pass one mum and back to maximuml twice `per revolution only ofthe varying beat frequencies produced at the frequency sweep willV go'backwards and forthe-mixer stage, means for producing frequency wards three times-per second forthe stated speed dependent voltage varying in dependency upon 40 of 90 R.P.M.

the vfrequency of said' output, a rectifier circuit The output from the mixer-2 will consist of the havingterminals forthe inclusion ofthe device sum and difference frequencies. This output is orjnetwork'to be tested and fed with said output fed to a low pass filter 5 which passes the differso that the current in said rectifier circuit is deence frequency only so that the filter output will pendent upon the impedance of said device or consist of Ya frequency varying continuously from network' and means for taking olf (for use in an 1 to 2l mc./s. and back again.- Part of the lter oscillographl) the frequency dependent voltage output is tapped off to control an AVC network 6 andvoltage proportional to the current in the of any knowntype which operates on the nxed rectifier circuit. frequency oscillator Iy to `Ir'iaintain the filter out- Preferably the frequency dependent voltage is put-amplitude constant.v produced by a discriminator circuit fed with outl Output from the low pass lter 5 Vis also taken put from the lter. to a frequency discriminator 'l at which the volt- Preferably also a cathode ray tube oscilloage` developed across alcap'acity intof which the graph is employed in conjunction with an instruvarying frequency is vfed Vwith y'constant voltage is mentin accordance with this invention which picked olf. As tl 1 e 'frequencyvariesso will'4 the Output from the filter is also taken to a rec- I tifier circuit shown within the chain line square and including a pair of diodes I I, I2 each havingY its cathode I3 or |4 connected to one or other of the line output terminals of thefilter 5 (the` filter output circuit is shown as of the balanced type with its centre point earthed). Across each diode is connected a low value resistance I5 or I5 (say 50 ohms each) in series with a condenser |'I or I8 adjacent the anode I9 or 20, the reist- ,4 in the oscillograph need not be rectilinear; for some purposesa logarithmic law is to be preferred arid,"ifdesired, provision may` be Vmade of apparatus capable of giving either a logarithmic or rectilinear law at will by operation of a switch.

For example Ithe horizontal sweep could be controlled by an amplifier including logarithmic law lcircuits which could be switched out when deance-condenser junction points 2| or 22 being connected through suitable switches (not shown), to terminals 24, 25 to which an impe-dance or device (not shown) to be tested may be connected.

The anodes I9, are connected each through a decoupling resistance 26 or 21, to a common' point which is taken to earth through a load re-` sistance 28 and a variable tap 29 on this resistancre 28 is taken through a two position switch 3|] toan amplifier 3| whose output is passed to thev vertical deflection plates 32 of the oscillograph I0. It will be seen that since the low value resistance elements I5, I5 are in series with the impedance or device connected to terminals 24 and under test and since the voltage input amplitude to the rectifier network is constant, the high frequency voltage appearing across the said low resistances will depend upon the ratio of the test impedance thereto. The D. C. component of the rectified H. F. voltage across the low resistances I5, I6 appears over the decoupling resistances 26, 21 and the load resistance 28 from which, after suitable amplification at stage 3|,

it is passed to the oscillograph I0.

Output from the filter 5 is also taken to a. furtherlmixer circuit 33 receiving, its second Vinput from a 1A mc./s. oscillator 34 having a very high harmonic content, the mixer output being fed to theA amplifier 3|. This arrangement of elements 33--34 acts as a calibrating unit since relatively large voltages are produced in mixer 33 in the region within plus or minus 5 kc./s. of zero beat and thewhorizontal scale is sufficiently contracted in. practice effectively superimposing small vertical deflections on the horizontal trace of the cathode" ray tube every megacycle. The calibration maybe operated continually or it may be operated alternatively With the impedance measuring circuitry, an electronic switch arrangement beingV preferably employed to select one from the other.v

The apparatus is capable of being used simply as a source of constant voltage varying frequency oscillations by connecting thetest terminals 24, 25 to the apparatus under test. Transfer impedance measurements can then be made by connecting the cathode ray oscillograph to the output of the said apparatus under test, which output is connected to terminals 24 and 25 andY switch being put into its right hand positionin the drawing. With the switch in its left hand position and the apparatus under test connected to terminals 24, 25 admittance testsvmay be made.l

It is not essential that the variation of frequency of the oscillator 3 be mechanically obsired. Again it is not essential that a frequency discriminator be used to produce the horizontal sweep in the cathode ray oscillograph for this may be produced in other ways, e. g. by cyclically varying a potentiometer, across which a D. C. potential is applied, in synchronism with the means for cyclically varying the variable frequency oscillator.

If desired, means may be provided to enable alternate excursions of the cathode ray beam to portray different phenomenarfor example to produce=alternately a network admittancecurve anda frequency calibration scale. This involves afswitching arrangement for connecting the cathode ray tube input alternately to the admittance network whose curve is to be traced and the frequency calibrating network 33--34, such switching is best accomplished electronically, efg. by means of a discharge tube circuithaving two conditions of electrical stability (socalled "flipfflop circuit) between which it is Again the law o1' horizontal (time base) sweepfl triggered at each horizontally deflecting voltage excursion. Such an arrangement would be very convenient also for testing components of unknown characteristics, against a standard component for alternate traces couldtrace the curve illustrative of the standard and interlacing traces that of the test component.

While I haveillustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modifications may be made inthe several elements employed and in their arrangement without departing from thespirit and scope of the invention.

.What is claimed is:

l. A circuit arrangement for testing electric apparatus comprising, a set of terminals adapted varying in frequency to said rectifier circuit tov produce a unidirectional current therein varying in proportionto the characteristics of said electric apparatus, means to apply said current toA orie-defi'ecti'on-means of a binary indicatingV device, meansto derive a secondunidirectional current proportional to theA frequency variation oi"V saidV alternating voltage,v means to apply said second current to the remaining deflection means of saidl binaryindicating device, a calibrating circuitl including a fixedfrequency oscillator, means.

to applysaid alternating voltage to said calibrating circuit to obtain be'atfrequency currents.

at frequencies determined by said fixed fre'- quencyoscillator, and means to superimpose said beat frequency currents on one of said unidirectional currents, thereby` to obtain a directly callbrated indication of the response of said' electric apparatus with respect to frequency. l

2. A circuit arrangementrfor testing electric* apparatus comprisinga pair of terminals adapted to'have said electric apparatus connected thereto,l a rectifier circuit coupled to said terminals, means" to apply an alternating voltage, cyclicallyvaryingu'i'n frequency to saidrectiii'rrcircuit to produce p au'nidirectional current therein varyingV in proascenso;

portion tothe impedance of said electricjappara- Y: tus, means to apply said-current to one deflecting means of a binary indicating device, means to Y derive a second unidirectional current proporto frequency, and means to producenan Yindica-- tion of calibration directly on'- the firstsaidindi-l cation, said means comprising a generatorof oscillations of fixed frequency, ,means to combine said alternating voltage and said Yoscillation of fixed frequency to obtain beat frequencylcurrents at frequencies spaced vapart at said fixed fre- V quency, and means to superimpose said;beat fre-A g f. Saidv undfeteilal; @lirquency currents on one rents.

3. A circuit arrangement fon testing electricapparatus comprising, a pair of terminals -adapted to have said electric apparatus l connected thereto, a rectifier circuit coupledto said termi-'- y. nais, means to apply an alternating voltage cy- 4 clically varying in frequency to said rectiiiercir--v cuit to produce a unidirectional current therein varying in proportion to the impedance of said electric apparatus, meansto apply 'said current to one deflecting means of a binary indicating device, means to derive a second unidirectional ,current proportional to the frequency variation of said alternating voltage, means to apply said second current to the remaining deiiecting means; of said binary indicating device, a Calibrating circuit including a fixed frequency oscillator, ymeans to apply said alternating voltageto said calibrating circuit to obtain beat frequency currents ,at frequencies determined by said fixed frequency oscilr lator, and means to superimpose said beat frequency currents on the first said unidirectional current thereby to obtain directly calibrated indication of the impedance of said electric apparatus with respect to frequency.

4. A circuit arrangement for testing electric apparatus, comprising a pair of terminals adapted to have said electric appartus connected thereto, a rectifier circuit, a rectifier element, an input resistor having one termination thereof connected to the cathode of said rectier element and the other termination thereof connected to one of said terminals, a capacitor joining said one terminal to the anode of said rectifier element, and a load resistor connected between a point of fixed potential and the anode of said rectifier element, means to apply an alternating voltage cyclically varying in frequency to said rectifier circuit at the cathode of said rectifier element to produce a current in said load resistor varying in proportion to the impedance of said electric apparatus, means to apply said current to one deflecting means of binary indicating device, means to derive a second current proportional to the frequency variations of said alternating voltage, means to apply said second current to the remaining deiiecting means of said binary indicating device, a Calibrating circuit including a fixed frequency oscllator, means to apply said alternating voltage to said Calibrating circuit to obtain beat frequency currents at frequencies determined by said fixed frequency oscillator, and means to superiinpose said beat frequency currents on the first said unidirectional current, thereby to obtain a directly calibrated indication of the impedance of said electrical apparatus with respect to frequency.

Y 5:1'Acircuit-arrangement'for4 testing electric apparatus comprising a pair of terminalsadapted to have said electric apparatus. connected thereto, a'rectifier circuit,iapair. of rectifier elements, inputresistors having'onetermination thereof connected to Ythe cathodes foff'saidf .rectifier elements.

and; the, other* termination; thereof 1 connectedto said= terminals, -capacitors .joining said terminals to theanodeslof said rectifierxelements,output resistors ihaving one termination thereof connected' tofthe anodesof said rectifier elements and the other terminations joined together anda load vresistor connected betweenfa point of fixed potential and :said'joinedloutput resistors, means to apply .fan alternating voltage Vcyclically varyingin rfrequencyto'saidJ rectifercircuit at the cathodes of said'frectifie'r elements 'to produce at potential across'said load Sresistorvarying in'pro` portion to the impedance Tof saidelectric apparatus, 'means to apply said 'potential toi one deiiectl ing'means iofbinary indicating device', means to" derive'a second potential proportional'to the'fre# quency.' variations of said alternating voltage,

meansV toappl-y said second lpotential to the re'- tain beat frequency potentials ait-'frequencies determined by 'said' fixed frequency oscil1ator', and

means fto superimpose 'saidf beat frequency poten@` tial-.on the-.potential across said load resistor` thereby to 'obtain' a directly calibrated'indication of the impedance of said electrical apparatus -vvith respect to frequency.`

A6. A circuit arrangement for testingV electric` apparatus, comprisingalpairof terminals adaptedv to have said electricapparattfsconnected 'theri to, a rectifier circuit, a pair of diode electron discharge tubes, input resistors having one termination thereof connected to the cathodes of said diode tubes and the other termination thereof connected to said terminals, capacitors joining said terminals to the anodes of said diode tubes, output resistors having one termination thereof connected to the anodes of said diode tubes and the other terminations joined together and a load resistor connected between a point of fixed potential and said joint output resistors, means to apply an alternating voltage cyclically varying in frequency to said rectifier circuit at the cathodes of said diode tubes to produce a current in said load resistor varying in proportion to the impedance of said electric apparatus, means to apply said current to one def'lecting means of a binary indicating device, means to derive a second current proportional to the frequency variation of said alternating voltage, means to applysaid second current to the remaining defiecting; means of said binary indicating device, a cali-N brating circuit including a fixed frequency osci1.

lator, means to apply said alternating voltage to:

said calibrating circuit to obtain beat frequencycurrents at frequencies determined by said fixedV frequency oscillator, and means to superimpose said beat frequency currents on said current ini said load resistor, thereby to obtain a directly calibrated indication of the impedance of saidl electrical apparatus with respect to frequency.

7. A circuit, arrangement for testing electric apparatus, comprising a pair of terminals adapt-- ed to have said electric apparatus connected thereto. a rectifier circuit, a pair of diode electron discharge tubes, input resistors having one termination thereof connected to the cathodes of said diode tubes and the other terminationthereof connectedk to said terminals,` capacitors'joining said terminals to the anodesof said diode tubes, output resistorshaving one.: termination thereof connected to the anodes ofsaid diode tubes and the yother terminations joined vtogether and a load resistor connected betweenza point' ofv fixed po tential and said Joined'outputv resistorameans :to

apply an alternating,vo1tage;,cyclical1y,varying in. frequency to said rectifier circuit at the..cathodes;

of said diode tubes torproduce acurrent'in'saidl load resistor varying inproportion` to rthe imped-V ance. of said .electric apparatus, means to apply Calibrating circuit -to obtain. beat frequency -currents at frequencies determined bysaid iixedfree quency oscillator, and means to superimposelsaid beat frequency currents `onsaid current in said load resistor, thereby to obtain adirectly'calibrated display of the impedance of said electrical apparatus with respect to frequency.

8. A circuit arrangement for testing electric apparatus, comprising a p airof terminals .adapt-r ed to have said electric; apparatus connected thereto, a rectifier circuit,a pair of diodezelectronV discharge tubes, input resistors having one termi,-

nation thereof connectedfto thecathodesof said,y

diode tubes and the other termination thereof connected to said terminals,r capacitorsrjoining said terminals to theanodes of said diode-tubes,

output resistors having one vtermination thereofconnected'to the anodes of said diode tubes and to-applyY an alternating voltage cyclically varying inl frequency to said rectifier circuit at the cathodes of said diode tubes to produce a voltage across said'load resistor varying in proportion to the'impedance of said electric apparatus, means to apply said voltage to one pair of defiecting electrodes'of a cathode ray oscillograph, means toderive a second voltage proportional to the frequency variations of said alternating voltage, means to' apply said second voltage to the remaining pair of deecting electrodes of said cathodevray oscillagraph, a Calibrating circuit including-a xed frequency oscillator, means to apply saidv alternating voltage to said Calibrating circuit to obtain beat frequency voltages at frequencies 'determined by said fixed frequency oscillator,

means to superimpose said beat frequency voltages onrsaid voltage across said load resistor thereby to obtain a directly calibrated display of the impedance of said electrical apparatus with "respect to frequency.

WILLIAM OLIVER AGAR.

REFERENCES CITED The following references'are of record in the itfileY ofv this patent:

UNITED STATES PATENTS 

